Although there have been considerable gains in the surgical treatment of heart diseases, many patients who undergo cardiopulmonary bypass (CPB) surgical procedures are at considerable risk for damage to the Central Nervous System (CNS) primarily due to microemboli and ischemia. these are both possible adverse sequelae of extra-corporal circulation. In addition to frank clinical symptoms and grossly observable signs, findings from a number of areas of research (e.g., neuropathological, cerebrospinal fluid enzyme tests, and neuropsychological assessment) real that many coronary bypass surgery patients experience subclinical brain damage. While these effects are often subtle and may not interfere with an individuals's functioning in obvious ways, they appear to account for many of the patients' complaints of concentration and memory impairment. Although reported incidence rates vary, it appears that many studies have underestimated this problem because sensitive measures of memory and other intellectual abilities have not been used. Also, studies that have used intellectual measures of outcome are methodologically weak, especially in the area of choice of memory tests. As memory tests. As memory complaints are the most frequently reported by patients, greater emphasis should be given to the assessment of memory functions, particularly those involving recall. The proposed study has 3 objectives: (1) to compare the neuropsychological functions of CPB-assisted cardiac surgery patients with a comparison group of general thoracic surgery patients who did not undergo CPB; (2) within the CPB cardiac group, to compare the effects of bubble versus membrane oxygenators on neuropsychological outcome measures; and (3) to identify some of the risk factors for CNS complications after open-heart surgery. Risk factors will be derived and variations in surgical procedure, such as the amount of time the patient was placed on the coronary bypass machine. Patients will be randomly selected from consecutive referrals for CPB surgery. They will be assessed on a battery of neuropsychological tests, outlined in this proposal, 1-2 days before surgery and at their usual surgical follow-up appointment, 6 weeks after surgery. Group comparisons between CPB vs thoracic surgery and bubble vs membrane oxygenator will be made using repeated measures analysis of variance. The relationship between risk factors and neuropsychological outcome will e examined using multiple regression techniques.